1. Field of the Invention
The present invention relates to a sealing mechanism in a Stirling engine and in particular to a sealing mechanism for preventing the invasion of operating fluid into an operating space in a Stirling engine.
2. Description of the Prior Art
A conventional sealing mechanism in a Stirling engine is shown, for example, in Japanese Patent Laid-open Print No. 64-87854 published on Mar. 31, 1989 without examination. The conventional sealing mechanism, which is served for preventing oil-invasion from a crank chamber to a back-space of a piston, includes a first seal member positioned at a side of the crank chamber and a second seal member positioned at a side of the piston. With respect to the first seal member, a sealing ability against the fluid-flow from the crank chamber to the back-space is superior to the counter fluid-flow. With respect to the second seal member, a sealing abilities are contrary or reversed to those of the first seal member. A space is defined between both seal members and is kept at a pressure which equals the minimum pressure of the back-space.
However, the conventional sealing mechanism has drawbacks as detailed hereinbelow. That is to say, an amount of oil corresponding to its oil-thickness on the piston are remained thereon and are moved toward the second seal member. In light of the foregoing abilities of the second seal member, unless the distance between both seal members is set to be greater than the stroke of the piston, the oil is moved into the back-space when the piston is in its upper dead-point. The resulting oil is scraped into the back-space by the second seal member when the piston is moved toward its lower dead-point. This phenomenon is called as the pumping-up phenomenon. In order to prevent the pumping-up phenomenon, the distance between both seal members has to be extended or enlarged. This means the enlargement of the Stirling engine.
In addition, since the space defined between both seal members is kept at a pressure of the minimum pressure of the pressure-variation in the back-space, if the Stirling engine is driven under its minimum-pressure to its maximum, excess pressures are applied to the seal members, thereby weaking the durability of each seal member and increasing the sliding friction between the piston and each seal member.